"Stupid things Windows does."
Users are using an ActiveX control in a web-based application. About once every 30 minutes, +/-30 minutes, they get a popup telling them that they've disconnected from the internet, and would they like to continue to work offline?
Reconnecting reconnects them.
Systems are all Windows XP, patched to the gills.
Guess what solved it?
Install Windows Media Player 9.
Don't ask me why.